The present invention is related to epoxy resin compositions and to a curative for epoxy resins and a curing accelerator for epoxy resins, both of which contain a tetrakisphenol compound.
Epoxy resins are characterized as one having various excellent properties, such as chemical proof, corrosion resistance, mechanical property, thermal property, adhesive property to various materials, electric property, and easy handling property under any condition, and are widely used for adhesives, paints, electrometal materials and complex materials. An epoxy group in an epoxy resin is a functional group which has great distortion therein and enormous reactivity, being reactive to both acids and bases, and is capable of curing epoxy resins by virtue of such high reactivity to make a resin into three dimension structure. An epoxy resin composition is composed of an epoxy prepolymer, which contains more than 2 epoxy groups in a molecule, and a curative, and is normally added with a curing accelerator, a denaturant, a filler, etc. depending upon the use thereof. It is known that the property of a cured-resin is subject to the type of a curative used, and various curatives have ever been used for industrial purposes. Epoxy resin compositions can be divided into two main types, the one is one-pack mixture and the other is two-pack mixture type, the former type can be cured, for example, by heating, pressing or allowing the composition itself to stand. The other type, two-pack mixture type, can be cured by admixing the main component and either a curative or a curing accelerator just before use and subsequently heating, pressing or allowing the mixture to stand, for example. Normally, the epoxy resin compositions are prepared into two-pack mixture-types, which are widely used for parts to be used in the fields of electric appliances industry, automobile industry and aircrafts industry, since two-pack mixture type has excellent properties in terms of the strength of cured-products, thermal property, electricity property, etc., though it is not easy to handle and not economical from operation point of view. However, the two-pack mixture type has problems that, (1) since it has short pot life, that means time maintainable the state of prepared composition to be usable for curing, operational performance is ceased due to starting of partial curing of the composition during the preparation, which causes the increase of viscosity of the composition, and (2) the physicochemical property of the composition is ceased by incorrect mixing or incomplete preparation. Therefore, latent-type curatives and curing accelerators, which are prepared as one-pack mixture type, have been desired. Latent-type curatives and curing accelerators are defined as ones, in which a curative and a curing accelerator compounded in a resin are stable at room temperature, and which may induce a curing reaction by virtue of an effect such as heating. For the initiation of curing reactions, heat, light, pressure, etc. may be effective, however, it is rather normal to use heating. For stabilizing the effect of curatives and curing accelerators, microcapsules thereof have been used, however, such microcapsules do not have sufficient mechanical strength, and therefore, there have been a problem in stability of those microcapsules such that they cannot stand for a process of blending to adjust resin compositions.
It is known that there are several types of curatives, for example, (1) addition-type curatives, the molecules of a curative are always incorporated into a cured-resin by virtue of the reaction with epoxy groups, (2) polymerization-type curatives, of which molecules enzymatically induce opening of rings of epoxy groups without causing incorporation of molecules of the curative into resins to cause polymerization and addition reaction between oligomers, and (3) photoinitiation-type curatives, which initiate curing by gaining irradiation of ultraviolet rays. Irrespective of the type as described above, it is the most important thing to carry on polymerization addition reaction under a fixed condition and more homogeneously and faster in order to obtain a cured-product in the stable state. However, we have still problems when using any of existing curatives such that (1) curing reaction by using any of existing curatives stops before the completion of the reaction due to increase of viscosity of resins, (2) there are many inhibitory factors against a curing reaction, (3) some severe conditions are required for completing a curing reaction, and (4) a great amount of a curative is required for carrying out a curing reaction homogeneously, and therefore, curing accelerators which enable to proceed homogeneous and fast polymerization addition reaction under a mild condition have badly been required. The curing accelerator is defined here as the one which makes the curing time of a curative for curing epoxy resins shorter and makes the curing reaction faster and more smooth. For addition-type curatives, such as primary amines and secondary amines, alcohols or phenols are used as a curing accelerator for promoting a polymerization-addition reaction. However, there is yet a problem in those use in general, since in case of using any of polymerization-type curatives, such as imidazoles, anion polymerization to be developed between oligomers tends to be inhibited by such alcohols and phenols.
In Japanese Patent Laid-open No. Hei 5-194711 Gazette, an epoxy resin which is compounded with a clathrate comprising both a curative for epoxy resins and a curing accelerator for epoxy resins with a multimolecular (phenol) host compound is described. Specifically, a method for curing epoxy resins by adding a clathrate comprising 2-ethyl-4-methylimidazole and 2,2xe2x80x2-methylenebis(4-methyl-6-t-butylphenol) at a ratio of 1:1 is added into an epoxy resin at a rate of several % based on imidazole is described in the Gazette.
However, although there is a description that a pot life (stability as a one-pack mixture) of the compounded-epoxy resin described above can be prolonged sharply, it is just a comparison with a similar clathrate, cyclodextrin, and the performance of that compounded-epoxy resin is not yet satisfactory for the use in a practical scale. Also, there is no description on the thermal stability and the curability at low temperature in the Gazette.
In Japanese Patent Laid-open No. Hei 5-201902 Gazette, there is a description of a clathrate comprising a tetrakisphenol compound and an imidazole compound, although there is no definite description that the clathrate can be used as a curative and a curing accelerator for epoxy resins.
In Japanese Patent Laid-open Nos. Sho 60-40125 and Hei 8-151429 Gazettes, an use of a salt of an imidazoline compound and a polyhydric phenol as a curative for epoxy resins is described. However, such curative is neither crystalline solid nor a clathrate and does not give sufficient stabilizing effect as a one-pack mixture, in practice. Again, in U.S. Pat. No. 3,519,576, an use of a salt of an amine compound and a polyhydric phenol compound as a curative for epoxy resins is described. However, this salt is not practically satisfactory as a curative in the light of the stability as a one-pack mixture. In U.S. Pat. No. 4,845,234, an use of a salt of an imidazole compound and a polyhydric phenol compound as a curative for epoxy resins is described. However, the state of this salt is highly-viscous liquid and is not a clathrate compound, and it is not the one which can be practically used with satisfaction in the light of the stability as a one-pack mixture.
In Japanese Patent Publication No. Hei 6-9868, a disclosure of the use of a salt of a tetrakisphenol compound and an imidazole compound as a curative for epoxy resins is made, however, there is no definite description about the use. In this publication, a salt of an imidazole compound and a polyhydric phenol compound is disclosed, however, the state of the salt is highly-viscous liquid and is not formed as a clathrate compound. Though there is a description as to the stability as a one-pack mixture, etc., such effect seems to be practically unsatisfactory. Furthermore, the description lacks an explanation on the heat stability and the curability at low temperatures.
In Japanese Patent Publication No. 2501154 and Japanese Patent Publication No. Hei 7-74280, there is a description that a tetrakisphenol skeleton be introduced into a produced-resin by using a tetrakisphenol compound as a curative. In this case, there is a characteristic in the resin that a tetrakisphenol skeleton be introduced into the produced-resin, where the tetrakisphenol compound as a curative is used at a greater rate of 0.5-2 moles against 1 mole of epoxy groups. As the effect, only description on the stability as a one-pack mixture is given, whereas no description is given about the stability on heat and the curability at low temperatures.
Considering such background as described above, it is an object of the present invention to provide a curative for epoxy resins and a curing accelerator for epoxy resins, which have improved subliming property and decomposing property, remarkably-improved thermal stability which is extremely important for the control of a curing reaction, a prolonged pot life (stability as a one-pack mixture comprising an epoxy resin and a curative) and improved curability at low temperatures. Furthermore, the present invention is also directed to provide an epoxy resin composition which provides stable cured-products even under a mild condition by proceeding a curing reaction of an epoxy resin faster and smoothly, etc.
For solving the problem as described above, it is found that the thermal stability of a curative for epoxy resins and a curing accelerator for epoxy resins in an epoxy resin composition can be improved by including either the curative or the curing accelerator with a tetrakisphenol host compound, allowing the pot life of such curative and curing accelerator remarkably longer, and further improving the curability thereof at low temperatures.
Further, it is found by the inventors that a fast and smooth curing reaction of epoxy resins can be accomplished by simultaneously using a specific tetrakisphenol compound together with a compound which reacts with the epoxy group of an epoxy resin to cure the resin, and that stable cured-products can be obtained even under a mild condition for the reaction.
Therefore, the present invention is directed to a curative for epoxy resins, characterized that the curative is composed of a clathrate of a tetrakisphenol compound represented by a general formula [I]; 
wherein X represents (CH2)n, wherein n is 0, 1, 2 or 3, and R1 to R8 each represents hydrogen, a lower alkyl, optionally-substituted phenyl, halogeno or a lower alkoxy, and a compound which reacts with the epoxy group of an epoxy resin to cure the resin, and to a curing accelerator, characterized by being a clathrate comprising a tetrakisphenol compound represented by the general formula [I] shown above and a compound accelerating the curing of a compound which reacts with the epoxy group of an epoxy resin to cure the resin.
The present invention is directed to an epoxy resin composition characterized by containing at least one of a clathrate comprising a tetrakisphenol compound represented by a general formula I and a compound which reacts with the epoxy group of an epoxy resin to cure the resin and a clathrate comprising a tetrakisphenol compound represented by the general formula I and a compound other than the tetrakisphenol compound, which accelerates the curing of an epoxy resin, and preferably to an epoxy resin composition wherein said clathrate is contained at a content range of from 0.001 to 0.1 mole based on 1 mole of epoxy groups.
Furthermore, the present invention is also directed to an epoxy resin composition characterized by containing a curative which reacts with the epoxy group of an epoxy resin to cure the resin and a tetrakisphenol compound represented by a general formula [I]; 
wherein X represents (CH2)n, wherein n is 0, 1, 2 or 3, and R1 to R8 each represents hydrogen, a lower alkyl, optionally-substituted phenol, halogeno or a lower alkoxy, in an amount of from 0.001 to 0.1 mole based on 1 mole of epoxy groups.
As examples for the compound (curative) which reacts with the epoxy group of an epoxy resin to cure the resin and the compound (curing accelerator) accelerating the curing of the resin, amines imidazoles, amides, esters, alcohols, thiols, ethers, thioethers, phenols, phosphorus compounds, ureas, thioureas, acid anhydrides, Lewis acids, onium salts, active silica compounds-aluminium complexes, etc. are given, however, any ones can be optionally selected from the ones which are customarily and conventionally-used as a curative or a curing accelerator for epoxy resins without any constraints.
As amines, for examples, aliphatic amines, alicyclic and heterocyclic amines, aromatic amines, modified amines and the like can be used.
As examples for the aliphatic amines: ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, dipropylenediamine, dimethylaminopropylamine, diethylaminopropylamine, trimethylhexamethylenediamine, pentanediamine, bis(2-dimethylaminoethyl)ether, pentamethyidiethylenetriamine, alkyl-t-monoamine, 1,4-diazabicyclo(2,2,2)octane(triethylenediamine), N,N,Nxe2x80x2,Nxe2x80x2-tetramethylhexamethylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylpropylenediamine, N,N,Nxe2x80x2,Nxe2x80x2-tetramethylethylenediamine, N,N-dimethylcyclohexylamine, dimethylaminoethoxyethoxy ethanol, dimethylaminohexanol and the like can be given.
As examples for the alicyclic and heterocyclic amines; piperidine, piperidine, menthanediamine, isophoronediamine, methylmorpholine, ethylmorpholine, N,Nxe2x80x2,Nxe2x80x3-tris(dimethylaminopropyl)hexahydro-s-triazine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetraoxyspiro(5,5)undecaneadacto, N-aminoethylpiperadine, trimethylaminoethylpiperadine, bis(4-aminocyclohexyl)methane, N,Nxe2x80x2-dimethylpiperadine, 1,8-diazabicyclo(4,5,0)undecene-7 and the like can be given.
As examples for the aromatic amines, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, diaminodiphenylmethane, diaminodiphenylsulfone, benzylmethylamine, dimethylbenzylamine, m-xylenediamine, pyridine, picoline and the like can be given.
As examples for the modified polyamines, polyamines added with epoxy compounds, polyamines added by Michael reaction, polyamines added by Mannich reaction, polyamines added with thiourea, ketone-blocked polyamines and the like can be given.
As examples for other amines, dicyandiamide, guanidine, organic acid hydrazid, diaminomaleonitrile, amineimide, trifluoroboron-piperidine complex, trifluoroboron-monoethylamine complex and the like can be given.
As examples for the imidazole compounds, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-isopropylimidazole, 2-n-propylimidazole, 2-undecyl-1H-imidazole, 2-heptadecyl-1H-imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenyl-1H-imidazole, 4-methyl-2-phenyl-1H-imidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazolium trimellitate, 1-cyanoethyl-2-undecylimidazolium trimellitate, 1-cyanoethyl-2-phenylimidazolium trimellitate, 2,4-diamino-6-[2xe2x80x2-methylimidazolyl-(1xe2x80x2)]-ethyl-s-triazine, 2,4-diamino-6-(2xe2x80x2-undecylimidazolyl)-ethyl-s-triazine, 2,4-diamino-6-[2xe2x80x2-ethyl-4-imidazolyl-(1xe2x80x2)]-ethyl-s-triazine, 2,4-diamino-6-[2xe2x80x2-methylimidazolyl-(1xe2x80x2)]-ethyl-s-triazine isocyanuric acid addition products, 2-phenylimidazole isocyanuric acid addition products, 2-methylimidazole isocyanuric acid addition products, 2-phenyl-4,5-dihydroxymethylimidazole, 1,2-phenyl-4-methyl-5-hydroxymethylimidazol, 1-cyanoethyl-2-phenyl-4,5-di(2-cyanoethoxy)methylimidazole, 1-dodecyl-2-methyl-3-benzylimidazolium chloride, 1-benzyl-2-phenylimidazole hydrochloride, 1-benzyl-2-phenylimidazolium trimellitate and the like can be given.
As examples for the imidazoline compounds, 2-methylimidazoline, 2-phenylimidazoline and the like can be given.
As examples for the amide compounds, polyamides obtainable by means of polymerization of dimaric acid and polyamine can be given, and as examples for ester compounds, active carbonyl compounds, such as aryl and thioaryl esters of carboxylic acids, can be given. Further, as examples for phenol, alcohols, thiols, ethers and thioether compounds, phenol novolac, cresol novolac, polyol, polymercaptan, polysulfide, 2-(dimethylaminomethylphenol), 2,4,6-tris(dimethylaminomethyl)phenol, tri-2-ethylhexyl hydrochloride of 2,4,6-tris(dimethylaminomethyl)phenol and the like can be given.
Further, as examples for urea, thiourea and Louis acid type curatives, butylated urea, butylated melamine, butylated thiourea, trifluoroboron and the like can be given.
As examples for phosphorus-containing curatives, organic phosphine compounds, such as alkyl phosphines including ethyl phosphine and butyl phosphine, primary phosphines, such as phenyl phosphine, dialkyl phosphines, such as dimethyl phosphine and dipropyl phosphine, secondary phosphines, such as diphenyl phosphine and methylethyl phosphine, tertial phosphines, such as trimethyl phosphine and triethyl phosphine, and the like can be given, whereas as examples for acid anhydride type curatives, phthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, endomethylenetetrahydrophthalic anhydride, methylendomethyle netetrahydrophthalic anhydride, maleic anhydride, tetramethylenemaleic anhydride, trimellitic anhydride, chlorendic anhydride, piromellitic anhydride, dodecenylsuccinic anhydride, benzophenonetetracarboxylic anhydride, ethylene glycol bis(anhydrotrimellitate), methylcyclohexenete tracarboxylic anhydride, polyazelaic anhydride and the like can be given.
As examples for onium salt type and active silica compound-aluminium complex type curatives, aryldiazonium salts, diaryliodonium salts, triarylsulfonium salts, triphenylsilanol-aluminium complex, triphenylmethoxysilane-aluminium complex, silylperoxide-aluminium complex, triphenylsilanol-tris(salicylaldehydato)-aluminium complex and the like can be given.
In the present invention, the tetrakisphenol compound forming a clathrate compound with the curative or the curing accelerator as described above is a compound represented by a general formula [I]; 
wherein X represents (CH2)n, wherein n is 0, 1, 2 or 3, and R1 to R8 may be the same or each independently different, and which represents, for examples, hydroxy, a C1-C6 lower alkyl, such as methyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-hexyl and cyclohexyl, phenyl optionally-substituted with halogeno, a lower alkyl or the like, halogeno, such as fluorine, chlorine, bromine and iodine, or a C1-C6 lower alkoxy, such as methoxy, ethoxy and t-butoxy.
Any tetrakisphenols represented by a general formula [I] can be used in the present invention without any cobstraint, and the followings are given as the definite examples, those are 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-methyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-dimethyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-chloro-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-dichloro-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-bromo-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-dibromo-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-t-butyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-fluoro-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-difluoro-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-methoxy-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3,5-dimethoxy-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-chloro-5-methyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-bromo-5-methyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-methoxy-5-methyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-t-butyl-5-methyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-chloro-5-bromo-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis(3-chloro-5-phenyl-4-hydroxyphenyl)ethane, 1,1,2,2-tetrakis[(4-hydroxy-3-phenyl)phenyl]ethane, 1,1,3,3-tetrakis(4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-methyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-chloro-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-dichloro-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-bromo-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-dibromo-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-phenyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-diphenyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-methoxy-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-dimethoxy-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3-t-butyl-4-hydroxyphenyl)propane, 1,1,3,3-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)propane, 1,1,4,4-tetrakis(4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3-methyl-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3,5-dimethyl-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3-chloro-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3,5-dichloro-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3-methoxy-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3,5-dimethoxy-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3-bromo-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3,5-dibromo-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3-t-butyl-4-hydroxyphenyl)butane, 1,1,4,4-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl)butane and the like. These tetrakis phenol compounds can be used in either form of single or a combination of 2 or more thereof in the present invention.
The synthesis of a clathrate comprising a tetrakisphenol compound and either a compound which reacts with the epoxy group of an epoxy resin to cure the resin (a curative) or a compound accelerating the curing of the resin (a curing accelerator) can be achieved at high selectivity and a high yield, by adding a tetrakisphenol compound into liquid amine or imidazole compound, which are either a curative or a curing accelerator, to allow them to a reaction in case such amine and imidazole are liquid compounds, or by adding a tetrakisphenol compound into the suspension of much amine or imidazole in case they are solid compound, or by allowing a tetrakisphenol powder to a solid-phase reaction directly with such solid amine or imidazole. The clathrate according to the present invention is produced basing on a mechanism that the molecules of a guest compound penetrate into the space in the crystalline lattice constituted by the molecules of a host compound. Consequently, for a guest compound, easiness in such penetration might be determined by the size, the configuration, the polarity, the solubility, etc. of the molecules of a guest compound. The state of the clathrate prepared in the present invention is crystalline solid.
As examples for the uncured epoxy resins applicable for the present invention, publicly-known resins, for examples, bisphenol A-epichlorohydrin resin, multifunctional epoxy resins, alicyclic epoxy resins, brominated epoxy resins, and epoxy-novolac resins, which contain at least one epoxy group in the molecule, can be given.
The present invention is directed to an epoxy resin composition characterized in that the composition contains a clathrate comprising a tetrakisphenol compound represented by a general formula [1] and either a curative for epoxy resins or a curing accelerator for epoxy resins, such as amines and imidazoles as described above, as a curative for epoxy resins and/or a curing accelerator for epoxy resins.
The amount of the clathrate to be used may be same to the amount of curatives and curing accelerators commonly-used, such as amines and imidazoles, to prepare a clathrate, and it depends on a method for curing. In case of using addition-type curatives of which molecules are always contained in the cured-resin because of its reaction with the epoxy groups, a clathrate is normally prepared by using a curative in an amount ranging from 0.3 to 1.0 mole relative to 1 mole of epoxy groups, though it depends on requirements on the property of a desired resin. Whereas, in case of polymerization-type curatives or light initiation-type curatives, which causes polymerization and addition reactions between oligomers by inducing the ring opening of epoxy groups in a reagent fashion without causing the inclusion of the curative molecules into the resin, and in case of using the clathrate as a curing accelerator, the content of the clathrate can be sufficient even it is less than 0.2 mole relative to 1 mole of epoxy groups. Particularly in the present invention, by using a clathrate wherein a tetrakisphenol compound is used, it is possible to reduce the content of the clathrate to a small amount ranging from 0.001 to 0.1 mole, and further to a range of from 0.001 to 0.05 mole. Further, it is also possible to use such clathrates as single or by mixing 2 or more thereof.
When the curative for epoxy resins or the curing accelerator for epoxy resins comprising the clathrate according to the present invention is compounded with the uncured epoxy resin as described above, the thermal stability which is very important for the control of a curing reaction is remarkably improved when compared with the stability of the epoxy resin, wherein only the guest compound (a curative or a curing accelerator, such as amines and imidazoles, before being included) contained in the curative and the curing accelerator is compounded.
The curative for epoxy resins and the curing accelerator for epoxy resins according to the present invention have good resistance against humidity and does not cause the decomposition and sublimation thereof.
And, the resin compositions according to the present invention containing the clathrates as a curatives or a curing accelerator as described above have several excellent thermal properties. For the thermal properties of the resin composition, three properties, including the thermal stability at an ordinary temperature (stability as a one-pack mixture), thermal stability to heating at a temperature of from an ordinary temperature to a desired temperature for a curing reaction and thermal stability at a curing temperature, are required, The uncured epoxy resins compounded with the curative and the curing accelerator according to the present invention are very stable (having good stability as a one-pack mixture) under an ordinary temperature and are curable by just heating them up to a certain temperature to promptly produce a cured-product. The curing of the epoxy resin should not be initiated at a temperature below 80xc2x0 C. or around. However, the epoxy resin starts curing rapidly when temperature raised to a range of from 100 to 130xc2x0 C., which is normally desired for curing. In case of using known curatives and curing accelerators, curing of epoxy resins normally start gradually by heating even before a time that temperature reaches to a desired range for curing, which gives unfavorable effect to the cured-product. In addition, in case of using a known curative having relatively excellent thermal stability, the initiating temperature for curing comes into a higher range of from 150 to 180xc2x0 C. However, by using the curative according to the present invention, curing at a lower range of temperature can be done.
As described above, the present invention discloses that a tetrakisphenol compound and a curative for epoxy resins or a curing accelerator for epoxy resins produce a crystalline clathrate having excellent preserving property and that the epoxy resin composition containing the said clathrate has remarkably excellent thermal property.
Further, the tetrakisphenol compound that forms the said clathrate is a compound that is conventionally known as an addition-type curative.
However, the inventors of the present invention found that the tetrakisphenol compound itself has an excellent catalytic action for curing epoxy resins.
Therefore, the present invention is also understood that it is directed to an epoxy resin composition comprising a curative which reacts with the epoxy group of an epoxy resin to cure the resins and a tetrakisphenol compound represented by a general formula [I] in an amount of from 0.001 to 0.1 mole based on 1 mole of the epoxy groups; 
wherein X represents (CH2)n, wherein n is 0, 1, 2 or 3, and R1 to R8 each represents hydrogen, a lower alkyl, optionally-substituted phenyl, halogeno or a lower alkoxy.
Examples for both of the curatives used in the present invention and the tetrakisphenol compounds represented by a general formula [I] and used together with the curatives are as described above.
By using the epoxy resin composition according to the present invention containing a tetrakisphenol compound, various curing reactions can proceed faster and smoothly even under a mild condition, which allow to obtain stable cured-products, because of the excellent catalytic activity of a tetrakisphenol compound for curing epoxy resins, and the curing property of a resin composition can be extremely improved by using the inventive epoxy resin composition when compared to the curing by using a curative only.
As described above, by using the clathrate comprising a curative for epoxy resins, such as amine compounds and imidazole compounds, and a tetrakisphenol compound, as a curative for epoxy resins, it is allowed to obtain a resin compound which has excellent thermal properties, such as stability as a one-pack mixture, stability to heat and curability at a low temperature, even with a very small amount, because of double effects, that is release of the curative included in the clathrate by heating and demonstration of concurrent catalytic effect given by the tetrakisphenol compound.
In addition to the elements described above, it is also allowable to compound various additives, such as a plasticizer, an organic solvent, a reactive diluent, a filler, a bulking agent, a reinforcing agent, a pigment, a flame retardant, a thickener and a mold-releasing agent, into the epoxy resin composition of the present invention, if required.
The curative for epoxy resins and the curing accelerator for epoxy resins specified in the present invention can be suitably used for curing epoxy resins, such as for epoxy resin-type adhesives, sealants for semiconductors, laminates for printed boards, varnish, powder paints, casting materials and inks.